1. Field of the Invention
This invention relates to an electronic component of the type which comprises an electronic element (e.g. solid electroltic capacitor element, transistor chip, diode chip, IC chip, or etc.) enclosed in a thermosetting resin package.
2. Description of the Related Art
As is well known, a resin-packaged electronic component such as solid electrolytic capacitor, transistor, diode or IC comprises an electronic element enclosed in a thermosetting resin package from which a plurality of leads extend out. Such an electronic component is disclosed in Japanese Patent Publication No. 3(1991)-30977 for example.
In general, an electronic component is manufactured by a transfer molding method. Specifically, the electronic element together with the leads is clamped between a pair of mold members defining a mold cavity, and an amount of thermosetting resin (e.g. epoxy resin) in fluid state is injected in the mold cavity under a high pressure. The resin is first heated for hardening and then cooled to provide a final product.
With the prior art electronic component, the electronic element, the lead and the resin package all have different coefficients of thermal expansion. Thus, after performing the transfer molding described above, the resin package will inevitably have residual internal stresses due to a difference in thermal expansion between the electronic element, the lead and the resin package.
In use, since the electronic component is repetitively subjected to thermal loads, the residual internal stresses of the resin package may develop into cracks. In reality, the crack sometimes reaches the electronic element, in which case the resin package fails to provide a sufficient protection for the electronic element which may be very sensitive. For instance, the external mositure may permeate to the electronic element through the crack, consequently damaging or deteriorating the sensitive element.